1. Field of the Invention
The invention relates generally to the field of photographic cameras and, in particular, to a camera viewfinder mask that is adjustable so that the field of view of the viewfinder can correspond to any of several different film image formats.
2. Description of the Prior Art
Many cameras in the past have been provided with viewfinders that are adjustable to different settings to change the size of the field of view in accordance with the adjustment of a zoom lens or the substitution of lenses of different focal lengths. Typically such adjustments are made by means of a mask with two blades that are moved in opposite directions along a straight path diagonal to the rectangular viewfinder frame, as illustrated, for example in U.S. Pat. No. 2,157,548. In such viewfinders, the aspect ratio of the field of view, i.e. the ratio of its height to its width, remains unchanged. As also shown in the '548 patent, such a viewfinder can be provided with means for compensating for parallax when the subject is close to the camera.
In a similar type of device, as illustrated, for example, in FIGS. 2 and 11A of U.S. Pat. No. 5,255,030, the two blades are moved in opposite directions along a straight path that angled, but not truly diagonal to the frame. In this case, different frame aspect ratios may be obtained, but both the height and width of the frame are varied continuously in the same sense. Accordingly, such a device cannot provide two different formats with the same height or width or three formats that vary other than in the specific manner dictated by such a straight movement path.
It is also known to provide a camera viewfinder with an adjustable mask device in which two blades are moved in opposite directions relative to each other by irregularly shaped cam slots or the like to adjust the viewfinder field to several different aspect ratios, as shown, for example, in U.S. Pat. No. 5,345,285. This type of device, however, tends to be rather complicated and bulky.
Because the types of adjustment mechanisms disclosed in the foregoing '548, '030 and '285 patents use cam surfaces or equivalent means to move the masking blades continuously between their different settings, any error in the positioning of the adjustment means produces a corresponding error in the field of view that is visible in the viewfinder.
In the type of camera to which an adjustable viewfinder mask in accordance with the present invention is particularly well suited, another adjustable mask device is employed to mask the film in the exposure plane so that the image can be exposed selectively in any of several different formats. When this adjustment of the film masking means is carried out, it automatically effects the corresponding adjustment of the viewfinder mask. Accordingly, with the types of viewfinder mask adjusting devices previously described, the coincidence between the format exposed on the film and the field of view of the viewfinder is dependent on the accuracy of the mechanism that couples the two masking devices. This results in more complexity and higher costs than are desired, particularly in the case of relatively small and inexpensive cameras.